1. Field of the Invention
The present invention relates to ordnance and more particularly to methods and apparatus for providing shielding from fast moving projectiles.
2. Brief Description of Prior Developments
The prior art discloses various methods and apparatus for shielding or protecting potential targets, including surface vehicles, aircraft, gun emplacements, ships, troop concentrations and the like from projectiles.
U.S. Pat. No. 5,635,260 to Rudolf, et al. discloses an arrangement for protecting an armored vehicle from projectiles. Upon triggering of a module by a sensor which calculates the attack trajectory of the projectile, two plates which are oriented in mutually parallel relationship are flung apart by electromagnetic or preferably pyrotechnic means. The two plates are oriented approximately parallel to the attack trajectory, and one of the two plates is acullerated parallel to the attack trajectory and hits the approaching projectile thereby altering the angle of the indecence to reduce kinetic energy or trigger the warhead. Even if the projectile impacts against the vehicle, penetration of the vehicle armor may be avoided.
U.S. Pat. No. 5,824,941 to Knapper discloses another arrangement for protection from attack by projectiles. This arrangement consists of a wall which is constituted of explosives and is arranged obliquely relative to the firing direction below a wall facing towards the projectile. A foil consisting of an explosive for the formation of a or composite armor is equipped with a steel plate on one side thereof and with a glass plate or a glass fiber-reinforced plastic material plate on its other side. The composite armor forms chambers within a box structure such that, within any one chamber, a steel plate is always located opposite a glass plate. Collective foils of explosive are connected along their bottom sides with a transmission or transfer foil which is similarly constituted from an explosive.
U.S. Pat. No. 6,029,558 to Stevens et al. discloses a counter-terrorism, reactive personnel protection system which detects the presence of a conclusive shock wave or ballistic projectile as it approaches a designed personnel target. Before impact, an air bag is rapidly inflated and interposed between the destructive force and the target so as to provide a protective barrier. The air bag is constructed from ultra-high molecular weight polyethylene material, and serves to halt or redirect the detected destructive force and thereby protect the designated target from attack.
U.S. Pat. No. 6,244,156 to Stuer, et al discloses a blast shell which is launched as a defense against an attacking tail fin-stabilized projectile, such as, in particular, a KE penetrator, directed toward an object which is to be protected. Gas fumes and a reaction pressure blast wave from a fired blast warhead of the shell act principally on the tail region of the attacking projectile. The penetrator is thereby deflected from a trajectory in the attack direction so that the object under attack is either missed or at least is not hit in a head-on direction. The effectiveness of the attacking projectile is thereby reduced.
A need still exists, however, for a still more efficient means for protecting potential targets such as vehicles, aircraft, gun emplacements, ships and troop concentrations and the like from high speed projectiles.
High speed projectiles have a plasma sheath associated with them in flight. Laser radiation of a wavelength not absorbed by the atmosphere can couple to the plasma and be absorbed. The absorbed energy increases the temperature and therefore the pressure on one side of the projectile, thus providing a deflection force. The required transverse momentum is some fraction of the projectile momentum. Larger projectiles which have greater momentum have larger transverse areas so the applied force (F=xcex94pA) increases with area for the same pressure increase. Furthermore, larger projectiles are fired from longer ranges which provides greater lever arms for deflection, therefore requiring smaller angles of deflection. In addition assymetric drag force, may in turn deflect the projectile.
The present invention comprises a method for deflecting a projectile from an initial trajectory which takes advantage of this plasma sheaf. Such a projectile has a first surface area and a second surface area and moves through a gaseous atmosphere with a surrounding plasma sheath. This method includes the step of directing electromagnetic radiation toward the projectile, wherein the electromagnetic radiation has a frequency which is absorbed by the plasma sheath but is not substantially absorbed by the gaseous atmosphere. Ordinarily the electromagnetic radiation will be directed toward the first surface area of the projectile in preference to the second surface area of the projectile. The first surface area and the second surface area are in opposed relation to each other. For example, the first surface area may be an upper surface area and the second surface area may be lower surface. Alternatively, the first surface area may be a front area and the second surface area may be a side area. The electromagnetic radiation is preferably light from a laser. The electromagnetic radiation causes the plasma sheath to be heated. The plasma sheath may be considered to have a first section adjacent the first surface area of the projectile and a second section adjacent the second surface area of the projectile. A temperature differential between the first section of the plasma sheath and the second plasma sheath results from directing the electromagnetic radiation toward the first surface area in preference to the second surface area. This temperature differential results in a pressure differential between said first surface area and said second surface area. Accordingly a traverse momentum is applied to the projectile resulting in a transverse impulse. The transverse impulse results in a deflecting force. The projectile may be a self-propelled rocket, an externally propelled shell, or an air delivered bomb. A fast moving projectile, as that term is used herein, will mean that the projectile will ordinarily have a velocity of from about 300 m/sec. to about 1500 m/sec.